The division and analysis of the favorable reservoir depositional facies of the dengying formation Upper-sinian in southeastern Sichuan Basin

Since weiyuan gas field was found in Upper Sinian dengying formation which is in weiyuan structure of Sichuan basin in 1964, it hasn't been apparent breakthrough after exploration in semicentury .The article is based on measured sections and drilling cores observation of Upper Sinian dengying formation, combined with methods of petrology, sedimentary and structure geology, to analyse facies, microfacies and other carbonate platform sedimentary system comprehensively, and analyses facies distribution pattern with evolution process further. The primary subfacies of dengying formation in study area is restricted platform facies and tidal-lagoon facies, with intra-platform shoal. Sedimentary type like Supratidal zone, intertidal zone, subtidal zone, lagoon, oolitic beach and sandy beach is developed in microfacies. Longitudinal changes in microfacies can be observed in single well and united well sections. The distribution characteristic of every microfacies is analysed by using microfacies distribution pattern. The analysis in property of microfacies show that the reservoir property of intraplatform shoal is the best, and the tidal zone takes the second place. These will be the prior position in reservoir.